Considerable effort has been devoted recently to a new tool in semiconductor technology, laser annealing. Laser annealing involves heating localized areas of a semiconductor, most notably silicon, to or near the melting point of the semiconductor, and rapidly cooling the material. As typically practiced, the material annealed is amorphous and constitutes a region within or overlying single crystal or substantially oriented material, and the heated portion of the semiconductor regrows or re-orients epitaxially. The technique has been applied to fabricating a wide variety of semiconductor devices, and has been proposed in various forms for processing bulk semiconductor material as well. It can also be utilized advantageously with single crystal or polycrystalline semiconductor and/or for various alloying processes without epitaxial regrowth. See, for example, U.S. Patent application G. K. Celler-T. E. Seidel, Ser. No. 917,841, filed June 22, 1978. Laser annealing is a rapid, effective tool for semiconductor manufacture, and promises to find widespread commercial application in sophisticated future integrated circuit and related semiconductor technologies.
While epitaxial regrowth of laser annealed semiconductors produces crystal material of exceedingly high quality, the material does suffer a major shortcoming. Laser annealed material contains ubiquitous defects that are quenched into the crystal during rapid cooling. In silicon, there appear to be two dominant kinds of defects present, a one which introduces defect states at 0.19 eV below the conduction band, a second at E.sub.c -0.38. Both defects will anneal at about 700 degrees C., indicating that they are characteristic of quenched material. We postulate that they arise because the semiconductor is rapidly quenched from a high temperature condition. Whatever the mechanism, defects of this kind have been observed in both solid phase and molten phase laser annealed silicon. Similar defects have also been observed in other semiconductors.
These electrically active point defects impair the usefulness of laser annealed material for certain applications, notably for electroluminescent and photoelectric devices, because the defects are strong recombination centers for injected or photon generated carriers. They also impair the emitter injection efficiency of bipolar devices.
Defect mechanisms in semiconductors is a subject of widespread interest in semiconductor technology, and a variety of processes for treating specific defects have evolved. Hydrogen incorporation has long been known to have a marked effect on amorphous semiconductors, R. C. Chittick et al J. Electrochem. Soc. 116, 77 (1969). W. E. Spear et al Sol. St. Conm. 17, 1193 (1975). The proposed mechanism being reaction of dangling Si bonds with the H atom. Pankove correlated the photoluminescence efficiency of a-Si:H with the presence of atomic hydrogen. J. I. Pankove, Appl. Phys. Lett., 32, 812 (1978). More recently, it has been reported that hydrogen treatment of single crystal silicon improves the reverse bias leakage currents of p-n junctions. J. I. Pankove et al Appl. Phys Lett. 32, 439 (1978). Seager and Ginley (Appl. Phys. Lett. 34, 337 (1979)) have indicated that hydrogen plasma exposure reduces grain boundary recombination rates in polycrystalline silicon. In addition, hydrogen has been correlated with the electrical inactivity of swirl defects in silicon. de Kock et al, Appl. Phys. Letters, 27, p. 313 (1975).
In spite of this background, and of intense interest in these characteristic point defects in laser annealed material, no mechanism has been reported to date for avoiding the consequences of these defects, other than by high temperature annealing. It is evident that a relatively slow, high temperature annealing step detracts from the attractiveness of the laser annealing technique.